Solution processing of V2O5-WO3 composite films for enhanced Li-ion intercalation properties

We have employed a simple and novel solution processing method to prepare V₂O₅-WO₃ composite films which demonstrate enhanced Li-ion intercalation properties for applications in lithium-ion batteries or electrochromic displays. This solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). The V₂O₅-WO₃ composite films show enhanced Li-ion intercalation properties compared to pure V₂O₅ and WO₃ films. For example, at a high current density of 1.33 A/g, V₂O₅-WO₃ film with a V₂O₅/WO₃ molar ratio of 10/1 exhibits the highest capacities of 200 mA h/g at the first cycle and 132 mA h/g after 50 cycles, while pure V₂O₅ film delivers discharge capacities of 108 mA h/g at the first cycle and 122 mA h/g after 50 cycles. The enhanced Li-ion intercalation properties of the composite films are ascribed to the reduced crystallinity, the increased porosity and thus the enhanced surface area. Both the cyclic voltammogram and chronopotentiometric curves of the V₂O₅-WO₃ film with a molar ratio of 10:1 are distinctively different from those of pure oxide films, suggesting a different Li-ion intercalation process in the V₂O₅-WO₃ film with the molar ratio of 10:1.